In the first of these interrelated tales, Merlin falls dotingly in love with the maiden Sir Pellanor brought into court, Nineve. She is afraid to lie with Merlin because he is a devil's son, and in his company she is "ever passynge wery of him," but she hides her disgust in order to learn the secrets of his art. She travels with him to the court of Sir Ban, where Merlin predicts fame for Ban's son Launcelot. Afterward, through magic, Nineve seals Merlin in a cave.
Meanwhile, Arthur goes to war against a league of five kings. Since Arthur leaves for war in haste, in advance of his allies, the enemy has the advantage; but by pure luck, Arthur, Kay, Gawain, and Gryfflet encounter the five kings alone. Gawain advises flight, but Kay vows he'll kill two of the kings, evening the odds, and does so. Arthur and the other knights kill the remainder, and Guinevere gives Kay her formal and characteristic praise: he is well worthy of some lady's love.
The host of the five kings is easily destroyed, and the eight Round Table knights who die in this action are replaced. One of the knights elevated to Round Table status is Tor. At his advancement another minor knight, Sir Bagdemagus, is angry. He leaves the court, resolving not to return until he has proved his worth. He finds a sign of the Grail — evidence that he is right in his judgment of himself — and later finds the cave where Merlin is sealed up alive. Merlin tells him that no one but Nineve can free him, and Bagdemagus rides on.
The second tale treats Morgan le Fay's attempted murder of Arthur. Riding in pursuit of a great hart, Arthur, Accolon, and King Uriens come upon an enchanted barge, where they are given a feast, then shown to splendid beds. Through Morgan's magic, Morgan's husband, King Uriens, awakens in his wife's arms; Accolon, her beloved, awakens at the edge of an enchanted well; and Arthur awakens in the dungeon of the cowardly King Damas, who imprisons and starves errant knights in hopes of forcing one to fight for him against his brother, an honorable king of whom Damas is jealous.
Arthur agrees to fight for Damas in order to free the other knights. As Damas's overlord, he can punish him later. Meanwhile Accolon is given Arthur's sword and scabbard by Morgan, who loves him and hopes to make him king and herself his queen. She arranges it that Accolon fights for Damas's brother. Thus Accolon and Arthur fight, neither one knowing the other, with magic on Accolon's side. Nineve, knowing Morgan's plan, comes to Arthur's aid and he is able to defeat Accolon. Accolon dies a few days later.
Morgan, supposing Arthur dead, raises a sword to kill her husband in his sleep, but her son Ywain prevents the murder. Morgan steals back the magic scabbard Arthur has gotten from Accolon, and when Arthur pursues her she throws it in a lake. She meets Accolon's cousin, who is about to be executed on the charge of having seduced a knight's wife. She rescues him, murders the cuckolded husband, and makes Accolon's cousin (Manessen) her new defender.
In the third tale, Morgan sends a peace offering to Arthur — a mantle wrought of jewels. He is impressed but says nothing. Nineve, the Damsel of the Lake, advises him to ask the messenger from Morgan to put on the mantle herself. When she is forced to do so, the messenger bursts into flame and burns to ashes. In his fury Arthur banishes Morgan's son Ywain, suspecting him of complicity. Gawain leaves with him "for whoso banyshyth my cosyn jarmayne shall banyshe me."
As Gawain and Ywain ride through a forest they find twelve maidens spitting on a white shield. When they ask what this means, the maidens explain that the shield belongs to the knight Marhault, a man who scorns all women. Marhault draws near, and Ywain and Gawain fight him. When he has overcome them both, he does not kill them, but tells them that he has been falsely accused. The twelve maidens are enchantresses. The three knights resolve to ride together.
In the mysterious country of Arroy they find a fountain and three damsels, one old, one middle-aged, one young. The three damsels are here, they say, to guide errant knights to adventure. Each knight must choose a lady and ride with her for a year. Ywain takes the oldest, Marhault takes the next, and Gawain takes the youngest. Then each knight goes his separate way with his guide.
Sir Gawain is quickly abandoned by his lady: he avoids a fight she advises him to take upon himself. When later he does help the knight he was earlier advised to help, he betrays his trust. He tells the knight, Sir Pellas (son of the maimed king, Pellam), that he will win the love of his haughty lady for him; but Gawain lies with her instead. Pellas is tempted to kill Gawain for his treachery, but at last he merely leaves a sign that lie knows, then retires. Nineve avenges Sir Pellas by forcing his disdainful lady to dote on him and by freeing Pellas of his passion for her. By yet another spell, Nineve makes Pellas her own lover and they live together happily.
Marhault, riding with the middle-aged lady, avenges wrongs as a true knight should. He meets a duke who is a sworn enemy to King Arthur's court because Gawain long ago murdered the duke's seventh son. Marhault fights the duke and his remaining six sons, beats them, and gets their vow to drop the feud. Marhault fights afterward in a great tournament and wins the same prize Pellas won in another tournament. Finally, he fights a giant for the Earl of Fergus and destroys him.
Ywain, riding with the oldest damsel, wins a tournament prize (as did Pellas and Marhault), then fights two cowardly knights who have taken land by "extortion" or seizure. Ywain wins the fight but is so badly hurt that it takes him half a year to recover.
The three knights of Arthur's court come together again and learn that Arthur has repented of banishing Ywain. On the day of Pentecost — the day on which Arthur's knights each year renew their vow to live by Arthur's code — Gawain, Ywain, and Marhault, as well as Sir Pellas and Nineve, return to Camelot. Pellas and Marahult take first and second place, respectively, at Arthur's tournament, and for this, and also for their year's deeds, are honored by appointment to the Round Table. Only for love of Arthur does Pellas spare Gawain. He takes pleasure all the rest of his life in shaming Gawain at tournaments.
These three tales are developed together, without closing summaries or new beginnings, and thus must certainly have been intended to form a unit — a single episodic tale. At all events, their interrelationship is obvious. Nineve the Damsel of the Lake figures prominently in all three: it is she who seals Merlin in the earth alive, she who saves Arthur in the fight with Accolon, and she who saves and rewards Pellas after Gawain's betrayal. She seems to represent, in effect, combined prudence and loyalty.
Sir Gawain figures in the first and third tales. He offers cowardly, though not disloyal, advice in the first tale when he advises Arthur to flee the five kings, since the fight will be five against four. In the third tale, his cowardly and disloyal behavior contrasts with the behavior of Pellas, Marhault, and Ywain, all of whom fight for the right against heavy odds. (Gawain refuses a fight against multiple opponents, though his guide advises it; he enters no tournaments; and he betrays his trust both to a fellow knight and to a lady.)
All three tales centrally concern love-betrayal — Nineve's justifiable betrayal of Merlin; Accolon's unwitting yet consenting betrayal of Arthur and Morgan's thoroughly treacherous betrayal of both Arthur and Uriens; and, in the third tale, Gawain's betrayal of Pellas and his lady. These central betrayals occur within a pattern of lesser love-betrayals and refusals of love. Together, then, the three tales establish in dramatic terms the qualities of right and wrong love, or, more precisely, of true love, prudent or imprudent, versus jealous love, good or bad. Merlin's infatuation balances that of Pellas; Morgan's vicious love of Accolon balances Gawain's vicious lust; Pellas' nobly restrained jealousy parallels Bagdemagus' nobly restrained jealousy in another sphere and plays ironically against Gawain's jealous blood — loyalty to Ywain.